Wind turbines are generally classified into two groups based upon the orientation of the turbine axis of rotation. There are horizontal axis wind turbines and vertical axis wind turbines. Horizontal wind turbines are the traditional image when thinking of windmills. The rotor shaft and an electric generator are generally mounted atop a tower and are connected to a gear box that converts the slow rotation of the blades into a faster rotation for the electric generator. Horizontal axis wind turbines have the disadvantages of needing to be readjusted to face the wind with every shift of the wind direction and requires gearing, braking and feathering controls to transfer the torque to an off-axis generator and means to keep the rotational speeds within acceptable limits. These turbines are equipped with high wind shutdown features to avoid over speed damage. Vertical axis wind turbines, on the other hand, have blades mounted to a vertically extending rotor shaft and are favored in areas where winds constantly shift direction because the blades are not required to be rotated to face into the wind and where low winds occur because they require a slower wind speed to start generating electricity.
Each group of wind turbines has advantages and disadvantages. The main disadvantage of vertical axis wind turbines is drag created as the blades rotate into the wind even while a lift is being created on the opposite side. The turbulent winds located near the ground can cause excessive noise as well as torque and strain on the main rotor shaft and bearings. Other disadvantages are that they have only about half the efficiency of the horizontal axis wind turbines in large part because of the additional drag that they have as the blades rotate in to the wind.
The present invention overcomes disadvantages of vertical axis wind turbines by utilizing a tower configuration in which the wind driven blades and turbine are inside a tower frame. The tower frame has diverter doors that reduce the draft of the blades as they rotate into the wind. The doors transfer the load of the blades to the tower and off the axis. This increases bearing life and ease in maintenance and repairs. Diverter doors also control the quantity of wind to the blades and therefore can increase wind to the blades in low wind conditions and will decrease wind in high wind conditions using computer control motors on the diverter doors. The tower configuration with the diverter doors, which can be fully closed, allows for greater protection against high wind conditions. The tower configuration with diverted doors allows the vertical axis wind turbine to be configured for a multi-megawatt generation and allows the turbines blades, which can increase torque and allow for a gear box ratio to increase the speed of the generator. In addition, the increased torque and weight transfer of the axis to the tower allows the axis to be fitted with a fly wheel which limits over torque from gusts of wind and allows continuous electrical generation during lull periods. The rigid tower and diverter doors allow the wind turbine to be used in hurricanes and other high wind conditions by closing the diverter doors and the rigid frame.
The present wind turbine can be installed in a city or urban environment and allows for ease in connection to an electrical grid and the transfer of electricity to the consumer.
In the past, there have been a wide variety of vertical axis wind generators including the following U.S. patents. The Rice U.S. Pat. No. 6,984,899 is a vertical axis windmill for the generation of electric power utilizing wind which maintains a relatively constant rotational frequency of the shaft of the windmill. It uses two wind foils which extend radially outward from the blades to provide a scoop for pulling in more air than would normally be received by the blades. The wind foils direct the flow to the power producing part of rotation of the blades and close to control the wind flow to the blades.
The Elder U.S. Pat. No. 6,448,669 is for a vertical axis water turbine used to convert water kinetic energy into mechanical energy. A vertical axis wind turbine is mounted so that wind is compressed and directed to the rotor blades by a plurality of fixed stator blades. The Kato U.S. Patent Application Publication No. US 2009/0167027 is for a blade for a windmill and a windmill and wind power generator of the vertical axis type. The Tsipov U.S. Pat. No. 6,962,478 is for a vertical axis windmill having a wind turbine mounted inside a frame. A plurality of gate elements which are turnably connected to the frame are for the closing and opening of the openings in the frame by wind flowing substantially in a horizontal plane. The Williams U.S. Patent Application Publication No. 2009/0097960 is for a vertical axis windmill assembly.
The Kariya U.S. Patent Application Publication No. 2008/0131281 is for a vertical axis windmill with a guiding device which includes vertical plates which are fixed on the bottom of the base structure to the top of the rotor in an annular array. The Uchiyama U.S. Pat. No. 7,417,334 is for a wind power generation system which uses a permanent magnets and coils for generating electric power.
The Valsamidis U.S. Pat. No. 5,380,149 is for a wind turbine cross wind machine which has a circumferential arrangement of guide vanes around a centrally located rotor and having an arrangement of turbine blades in the middle so that the guide vanes can guide the wind falling upon a counteracting rotor blades towards the direction of rotor rotation.
The Taylor U.S. Pat. No. 6,015,258 and the Teasley et al. U.S. Pat. No. 4,318,019, and the Townsend U.S. Pat. No. 5,632,599 each teach wind turbine rotor blade designs.
The Rowe U.S. Pat. No. 6,740,989 is for a vertical axis wind turbine which has vanes surrounding a turbine rotor with each vane creating a turbulent swirling boundary layer on the vane surface that rotates in the direction that draws and redirects air flow into the air flow channels defined by the stator vanes. It is then compressed by the narrowing of the channels and directed to rotor blades to drive the turbine.
The Roberts U.S. Pat. No. 6,465,899 is for an omni-directional vertical-axis wind turbine. The Ouellet U.S. Pat. No. 5,126,584 is for a windmill having a stator and a rotor. The stator surrounds and supports the rotor and has equally spaced vanes having a stationary shutter surrounding a movable inner shutter capable of pivoting around the longitudinal axis.
The present invention is for a vertical axis wind turbine for generating electricity which has a vertically extending wind turbine having its rotor shaft connected through a gear box to an electric generator and which has a plurality of diverter doors which are movable to control the air flow to and from the wind turbine which doors are closable to protect the wind turbine to protect against winds exceeding a predetermined velocity.